This invention pertains to an improved reciprocating wiper system for motor vehicles. In particular, the invention pertains to such a system comprising a piston which is displaceably guided in a housing, and having a slide fixed on the piston in a manner protected against twisting. The slide projects radially from the piston and is longitudinally guided on a guide element fixed to the housing.
In many applications of a device of this kind the piston has to be guided in such a way that it cannot turn about its longitudinal axis during its adjusting motion. This applies also for so-called reciprocating wiper systems in which during the pendulum-type motion the windscreen wiper fixed on the piston is retracted and extended in the radial direction, so that the corner areas of a windscreen can also be reached by the wiper blade of the windscreen wiper.
German specification OS No. 3,409,256 describes a reciprocating wiper system in which a slide is fixed on the piston in a manner protected against twisting. The slide includes guide grooves in its diametrically opposite end areas. Guide elements fixed on the housing in the shape of flat rails engage the guide grooves. The depth of the grooves in the guide block is greater than the portion of the guide rails fittingly protecting into the said grooves. The guide rails may be considered as defining a plane. If in that plane the guide rails are not aligned accurately parallel to each other and parallel to the adjusting direction of the piston this does not affect the smooth running of the piston, because the guide rails can more or less dip into the grooves on the guide block. However if the guide rails were arranged in a skew wise manner, tightness of the piston could not be excluded in the case of a rigid connection between slide and piston. To prevent this disadvantage the slide is held on the piston to be movable in one direction, so that these detrimental tolerances with regard to the position of the guide rails can be compensated for. For this purpose the piston is formed as a pivot with cheeks at its end, which is put into a somewhat larger recess of the slide. Thus in these constructions tolerances of shape and position of the guide elements and of the slide which are unavoidable in practice are compensated for, so that the piston can be smoothly adjusted. This also has a favorable effect on the service life of a device of this kind. However it is true that the production of a protection against twisting for the piston is involved with considerable difficulties and costs. The guide elements have indeed to be worked in a special way in order to provide for the necessary smooth surface. This is very costly in the case of flat guide elements with the shape of rails. Because of the piston end formed as a pivot with cheeks it is also linked with considerable costs to produce a connection with play between piston and slide. The slide has a relatively complicated space form and it is therefore not either inexpensive to produce it. Furthermore additional elements are necessary to fix the slide in the adjusting direction.
Thus the present invention is based on the problem of simplifying a device of the initially mentioned kind with regard to a protection against twisting for the piston and improving it with regard to its guide properties.